Polycrystalline diamond (PCD) materials and PCD elements formed therefrom are well known in the art. Conventional PCD is formed by combining diamond grains with a suitable solvent catalyst material to form a mixture. The mixture is subjected to processing conditions of extremely high pressure/high temperature (HP/HT), where the solvent catalyst material promotes desired intercrystalline diamond-to-diamond bonding between the grains, thereby forming a PCD structure. The resulting PCD structure produces enhanced properties of wear resistance and hardness, making PCD materials extremely useful in aggressive tooling, wear, and cutting applications where high levels of wear resistance and hardness are desired.
Solvent catalyst materials typically used for forming conventional PCD include metals from Group VIII of the Periodic table, with cobalt (Co) being the most common. Conventional PCD can comprise from 85 to 95% by volume diamond and a remaining amount of the solvent catalyst material. The solvent catalyst material is present in the microstructure of the PCD material within interstices that exist between the bonded together diamond grains.
A problem known to exist with such conventional PCD materials is thermal degradation due to differential thermal expansion characteristics between the interstitial solvent catalyst material and the intercrystalline bonded diamond. Such differential thermal expansion is known to occur at temperatures of about 400° C., causing ruptures to occur in the diamond-to-diamond bonding, and resulting in the formation of cracks and chips in the PCD structure.
Another problem known to exist with conventional PCD materials is also related to the presence of the solvent catalyst material in the interstitial regions and the adherence of the solvent catalyst to the diamond crystals to cause another form of thermal degradation. Specifically, the solvent catalyst material is known to cause an undesired catalyzed phase transformation in diamond (converting it to carbon monoxide, carbon dioxide, or graphite) with increasing temperature, thereby limiting practical use of the PCD material to about 750° C.
Attempts at addressing such unwanted forms of thermal degradation in PCD are known in the art. Generally, these attempts have involved the formation of a PCD body having an improved degree of thermal stability when compared to the conventional PCD material discussed above. One known technique of producing a thermally stable PCD body involves at least a two-stage process of first forming a conventional sintered PCD body, by combining diamond grains and a cobalt solvent catalyst material and subjecting the same to high pressure/high temperature process, and then removing the solvent catalyst material therefrom.
This method, which is fairly time consuming, produces a resulting PCD body that is substantially free of the solvent catalyst material, and is therefore promoted as providing a PCD body having improved thermal stability. However, the resulting thermally stable PCD body typically does not include a metallic substrate attached thereto by solvent catalyst infiltration from such substrate due to the solvent catalyst removal process.
The thermally stable PCD body also has a coefficient of thermal expansion that is sufficiently different from that of conventional substrate materials (such as WC-Co and the like) that are typically infiltrated or otherwise attached to the PCD body to provide a PCD compact that adapts the PCD body for use in many desirable applications. This difference in thermal expansion between the thermally stable PCD body and the substrate, and the poor wetability of the thermally stable PCD body diamond surface makes it very difficult to bond the thermally stable PCD body to conventionally used substrates, thereby requiring that the PCD body itself be attached or mounted directly to a device for use.
However, since such conventional thermally stable PCD body is devoid of a metallic substrate, it cannot (e.g., when configured for use as a drill bit cutter) be attached to a drill bit by conventional brazing process. The use of such thermally stable PCD body in this particular application necessitates that the PCD body itself be mounted to the drill bit by mechanical or interference fit during manufacturing of the drill bit, which is labor intensive, time consuming, and which does not provide a most secure method of attachment.
Additionally, because such conventional thermally stable PCD body no longer includes the solvent catalyst material, it is known to be relatively brittle and have poor impact strength, thereby limiting its use to less extreme or severe applications and making such thermally stable PCD bodies generally unsuited for use in aggressive applications such as subterranean drilling and the like.
It is, therefore, desired that a diamond material be developed that has improved thermal stability when compared to conventional PCD materials. It is also desired that a diamond compact be developed that includes a thermally stable diamond material bonded to a suitable substrate to facilitate attachment of the compact to an application device by conventional method such as welding or brazing and the like. It is further desired that such thermally stable diamond material and compact formed therefrom have properties of hardness/toughness and impact strength that are the same or better than that of conventional thermally stable PCD material described above, and PCD compacts formed therefrom. It is further desired that such a product can be manufactured at reasonable cost.